Today's dishwashers are expected to perform high quality wash of items. Further, environmental concerns require an efficient use of water and energy during a wash cycle. The requirement of performing high quality wash of items and the requirement of efficient use of water and energy during a wash cycle puts requirements on spray arm arrangements for dishwashers. A spray arm comprising spray nozzles is usually rotatably arranged inside a washing chamber of a dishwasher to distribute a washing liquid, such as water and detergent, on to items in the dishwasher. The spray arm may be driven to rotate by the force of cleaning sprays from the spray nozzles. The spray arm may also comprise a dedicated drive nozzle adapted to create a driving force on the spray arm. During rotation of the spray arm within the washing chamber, the water and detergent is distributed on to the items with a pressure adapted not to harm glass or other delicate items. However, a limitation in spray pressure may lead to heavily soiled items like pots and pans not being properly cleaned. These items may thus require a second washing procedure to be sufficiently cleaned, leading to unnecessary waste of water. Further, items located in the dishwasher, such as cutlery, may block the rotation of the spray arm. A blocked spray arm will only distribute washing liquid over a limited region of the dishwasher, thereby wasting water and energy without performing washing action as intended.
Document DE 4020898 A1 describes a method of detecting a blocked spray arm using a rotation detecting sensor. The sensor provides a pulse signal every time the spray arm passes the sensor, which pulse signal restarts a countdown. If the spray arm is blocked the sensor will not provide the pulse signal and the countdown will not be restarted. When the countdown ends, the washing procedure will be ended in order to save washing fluid and reduce the risk of damaging the dishwasher. In one embodiment, the sensor comprises a deflecting wall, such as an elastic rubber membrane, arranged in a spray area of the cleaning spray from a spray nozzle. When the spray arm passes the deflecting wall the force of the spray causes the deflecting wall to deflect which causes the deflecting wall to activate a micro switch arranged in contact with the deflecting wall.
Thus, the method described in document DE 4020898 A1 requires modifications of the wall within the washing chamber and the use of a deflecting wall. Also, monitoring of rotation of the spray arm may be imprecise since the method is dependent on a spray hitting the deflecting wall. For example, if a spray nozzle is clogged, the spray may not reach the deflecting wall. In such case the method will not detect rotation of the spray arm, even though the spray arm may still rotate. Also, several neighbouring spray nozzles hitting the deflector wall may lead to an imprecise monitoring of rotation of the spray arm. Further, the deflector wall as described in DE 4020898 A1 may be sensitive to damages.
In view of the above, there is room for improvement of dishwashers comprising a spray arm arrangement.